The science behind mother and baby bonding and sexual chemistry between partners is to be explained in a St Valentine's Eve lecture.

Edinburgh brain expert Professor Gareth Leng will examine how the hormone oxytocin helps forge permanent ties between lovers, after the initial rush of excitement of a new relationship.

The hormone works by "changing the wiring" of billions of brain circuits.

Prof Leng is a neuroscientist at the University of Edinburgh.

Maternal behaviour

He will provide a breakdown of the brain's functions in relation to love during a lecture in London on Friday, 13 February entitled "How does a brain fall in love?"

According to Prof Leng, oxytocin helps bond a mother and her baby and is also released during both childbirth and orgasm.

He said it acts like a "master switch" in the brain, opening up new
patterns of interaction between nerve cells.

How a single, albeit prolonged, exposure to oxytocin can produce such
profound and prolonged changes in behaviour is not known, but we are trying
to find answers

Prof Leng

He also claims that people who have fewer of the special brain receptors needed to take up the oxytocin may have difficulties in making successful permanent bonds with their partners.

Research has found that the hormone, which is released into the brain in large amounts during labour and during sexual activity, is an important trigger of maternal behaviour in animals.

Its crucial role in sexual bonding has been observed by North American scientists studying the prairie vole.

Professor Leng said: "The prairie vole mates for life and this life-long bond is established over the 48 hours of intense mating activity that is its first experience of sex.

"During this time, large amounts of oxytocin are released within the brain. Prairie voles have oxytocin receptors in different parts of their brains, and scientists have found that blocking these receptors prevents the formation of pair-bonding in females.

"How a single, albeit prolonged, exposure to oxytocin can produce such
profound and prolonged changes in behaviour is not known, but we are trying
to find answers.

"Understanding this process is essential to understanding how drugs can influence mood and behaviour, for good or bad."